[PATCH v6 11/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities

From: Damon Ding <damon.ding@rock-chips.com>
To: andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org
Cc: Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se,
	jernej.skrabec@gmail.com, maarten.lankhorst@linux.intel.com,
	mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com,
	simona@ffwll.ch, shawnguo@kernel.org, s.hauer@pengutronix.de,
	kernel@pengutronix.de, festevam@gmail.com, inki.dae@samsung.com,
	sw0312.kim@samsung.com, kyungmin.park@samsung.com,
	krzk@kernel.org, alim.akhtar@samsung.com, jingoohan1@gmail.com,
	p.zabel@pengutronix.de, hjc@rock-chips.com, heiko@sntech.de,
	andy.yan@rock-chips.com, dmitry.baryshkov@oss.qualcomm.com,
	dianders@chromium.org, m.szyprowski@samsung.com,
	luca.ceresoli@bootlin.com, jani.nikula@intel.com,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org,
	linux-rockchip@lists.infradead.org,
	Damon Ding <damon.ding@rock-chips.com>
Subject: [PATCH v6 11/18] drm/display: bridge_connector: Ensure last bridge determines EDID/modes detection capabilities
Date: Tue, 30 Sep 2025 17:09:13 +0800	[thread overview]
Message-ID: <20250930090920.131094-12-damon.ding@rock-chips.com> (raw)
In-Reply-To: <20250930090920.131094-1-damon.ding@rock-chips.com>

When multiple bridges are present, EDID detection capability
(DRM_BRIDGE_OP_EDID) takes precedence over modes detection
(DRM_BRIDGE_OP_MODES). To ensure the above two capabilities are
determined by the last bridge in the chain, we handle three cases:

Case 1: The later bridge declares only DRM_BRIDGE_OP_MODES
 - If the previous bridge declares DRM_BRIDGE_OP_EDID, set
   &drm_bridge_connector.bridge_edid to NULL and set
   &drm_bridge_connector.bridge_modes to the later bridge.
 - Ensure modes detection capability of the later bridge will not
   be ignored.

Case 2: The later bridge declares only DRM_BRIDGE_OP_EDID
 - If the previous bridge declares DRM_BRIDGE_OP_MODES, set
   &drm_bridge_connector.bridge_modes to NULL and set
   &drm_bridge_connector.bridge_edid to the later bridge.
 - Although EDID detection capability has higher priority, this
   operation is for balance and makes sense.

Case 3: the later bridge declares both of them
 - Assign later bridge as &drm_bridge_connector.bridge_edid and
   and &drm_bridge_connector.bridge_modes to this bridge.
 - Just leave transfer of these two capabilities as before.

Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 .../gpu/drm/display/drm_bridge_connector.c    | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index baacd21e7341..0ca6f140e85b 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -640,6 +640,7 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 	struct drm_connector *connector;
 	struct i2c_adapter *ddc = NULL;
 	struct drm_bridge *bridge, *panel_bridge = NULL;
+	struct drm_bridge *pre_bridge_edid, *pre_bridge_modes;
 	unsigned int supported_formats = BIT(HDMI_COLORSPACE_RGB);
 	unsigned int max_bpc = 8;
 	bool support_hdcp = false;
@@ -668,6 +669,9 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 	 */
 	connector_type = DRM_MODE_CONNECTOR_Unknown;
 	drm_for_each_bridge_in_chain(encoder, bridge) {
+		pre_bridge_edid = bridge_connector->bridge_edid;
+		pre_bridge_modes = bridge_connector->bridge_modes;
+
 		if (!bridge->interlace_allowed)
 			connector->interlace_allowed = false;
 		if (!bridge->ycbcr_420_allowed)
@@ -681,6 +685,44 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 			bridge_connector->bridge_detect = bridge;
 		if (bridge->ops & DRM_BRIDGE_OP_MODES)
 			bridge_connector->bridge_modes = bridge;
+
+		/*
+		 * When multiple bridges are present, EDID detection capability
+		 * (DRM_BRIDGE_OP_EDID) takes precedence over modes detection
+		 * (DRM_BRIDGE_OP_MODES). To ensure the above two capabilities
+		 * are determined by the last bridge in the chain, we handle
+		 * three cases:
+		 *
+		 * Case 1: The later bridge declares only DRM_BRIDGE_OP_MODES
+		 *  - If the previous bridge declares DRM_BRIDGE_OP_EDID, set
+		 *    &drm_bridge_connector.bridge_edid to NULL and set
+		 *    &drm_bridge_connector.bridge_modes to the later bridge.
+		 *  - Ensure modes detection capability of the later bridge
+		 *    will not be ignored.
+		 *
+		 * Case 2: The later bridge declares only DRM_BRIDGE_OP_EDID
+		 *  - If the previous bridge declares DRM_BRIDGE_OP_MODES, set
+		 *    &drm_bridge_connector.bridge_modes to NULL and set
+		 *    &drm_bridge_connector.bridge_edid to the later bridge.
+		 *  - Although EDID detection capability has higher priority,
+		 *    this operation is for balance and makes sense.
+		 *
+		 * Case 3: the later bridge declares both of them
+		 *  - Assign later bridge as &drm_bridge_connector.bridge_edid
+		 *    and &drm_bridge_connector.bridge_modes to this bridge.
+		 *  - Just leave transfer of these two capabilities as before.
+		 */
+		if (bridge->ops & DRM_BRIDGE_OP_EDID &&
+		    !(bridge->ops & DRM_BRIDGE_OP_MODES)) {
+			if (pre_bridge_modes)
+				bridge_connector->bridge_modes = NULL;
+		}
+		if (bridge->ops & DRM_BRIDGE_OP_MODES &&
+		    !(bridge->ops & DRM_BRIDGE_OP_EDID)) {
+			if (pre_bridge_edid)
+				bridge_connector->bridge_edid = NULL;
+		}
+
 		if (bridge->ops & DRM_BRIDGE_OP_HDMI) {
 			if (bridge_connector->bridge_hdmi)
 				return ERR_PTR(-EBUSY);
-- 
2.34.1


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